This invention is generally directed to photoresponsive imaging members or devices, and more specifically, the present invention is directed to an improved layered photoresponsive device with hole transport layers comprised of certain novel compositions of matter possessing an aromatic ether linkage, including sulfur and oxygen ethers, which compositions have improved solubility and desirable compatibility with the polymeric binder resinous substances within which they are dispersed. Accordingly, in one embodiment of the present invention there are provided improved overcoated photoresponsive imaging members comprised of a photogenerating layer, and in contact therewith a hole transport layer containing therein the novel aromatic ether compositions illustrated herein. There is further provided in accordance with the present invention overcoated photoresponsive devices containing a hole transport layer comprised of the aromatic ether compositions described, situated between a photogenerating layer and a supporting substrate, and also there are provided layered overcoated photoresponsive devices sensitive to visible light and infrared radiation comprised of a photogenerating layer, a photoconductive layer, and a hole transport layer containing the aromatic ether compositions of the present invention. The photoresponsive imaging devices of the present invention are useful in various electrostatographic imaging systems, including xerographic imaging systems, and xerographic printing systems, wherein high quality images are obtained.
Electrostatographic imaging processes, which are well known, involve the formation and development of electrostatic latent images on the surface of photoconductive materials referred to in the art as photoreceptors or photosensitive compositions. In these imaging systems, and in particular in xerography, the xerographic plate containing the photoconductive insulating layer is imaged by uniformly electrostatically charging its surface, followed by exposure to a pattern of activating electromagnetic radiation such as light, thereby selectively dissipating the charge in the illuminated areas of the photoconductive member causing a latent electrostatic image to be formed in the non-illuminated areas. This latent electrostatic image can then be developed with compositions containing toner particles and carrier particles, followed by subsequently transferring this image to a suitable substrate such as paper. Many known photoconductive members can be selected for incorporation into the electrostatographic imaging system including, for example photoconductive insulating materials deposited on conductive substrates, as well as those containing a thin barrier layer film of aluminum oxide situated between the substrate and the photoconductive composition. The barrier layer is primarily for the purpose of preventing charge injection from the substrate into the photoconductive layer subsequent to charging, as injection could adversely affect the electrical properties of the photoreceptor compositions involved.
Examples of photoconductive members include those comprised of inorganic materials and organic materials, composite layered devices containing inorganic or organic substance, layered devices containing photoconductive substances dispersed in other materials, and the like. An example of one type of composite photoconductive layer used in xerography is described, for example in U.S. Pat. No. 3,121,006, wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In a commercial form, the photoconductive composition involved is comprised of a paper backing containing a coating thereon of a binder layer comprised of particles of zinc oxide uniformly dispersed therein. Useful binder materials disclosed include those which are incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result, the photoconductive particles must be in substantially contiguous particle to particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, about 50 percent by volume of photoconductive particles is usually necessary in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. These high photoconductive concentrations can destroy the physical continuity of the resin particles, thus significantly reducing the mechanical strength of the binder layer.
Illustrative examples of specific binder materials disclosed in the '006 patent include, for example polystyrene resins, silicone resins, acrylic and methacrylic ester polymers, polymerized ester derivatives of acrylic and alpha-acrylic acids, chlorinated rubber, vinyl polymers and copolymers, and cellulose esters.
Other known photoresponsive compositions include amorphous selenium, halogen doped amorphous selenium substances, amorphous selenium alloys, including selenium arsenic, selenium tellurium, selenium arsenic antimony, halogen doped selenium alloys wherein the halogen is a material such as chlorine, iodine or fluorine, cadmium sulfide and the like. Generally, these photoconductive materials are deposited on suitable conductive substrates and incorporated into xerographic imaging systems for use as imaging members.
Recently there has been disclosed layered photoresponsive devices comprised of photogenerating layers and transport layers, deposited on conductive substrates as described, for example, in U.S. Pat. Nos. 4,265,990; 4,233,383; 4,281,054 and 4,415,639; and overcoated photoresponsive materials with a hole injecting layer, a hole transport layer, a photogenerating layer and a top coating of an insulating organic resin, as described, for example in U.S. Pat. No. 4,251,612. Examples of generating layers disclosed in these patents include trigonal selenium and various phthalocyanines, while examples of hole transport layers include certain diamines dispersed in inactive polycarbonate resin materials. The disclosures of each of these patents are totally incorporated herein by reference.
Additionally, there is disclosed in Belgium Pat. No. 763,540 an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting the photogenerated holes into a continuous second active layer containing a transport organic material. The organic material is substantially non-absorbing in the spectral region of intended use, however, it is active in that it allows the injection of photogenerated holes from the photoconductive layer and allows these holes to be transported through the active layer.
Other representative patents disclosing layered photoresponsive devices include U.S. Pat. Nos. 3,041,116; 4,115,116; 4,047,949 and 4,081,274.
Several of the above-described layered photoresponsive devices possess undesirable characteristics, for example, in these devices there is limited solubility of the hole transport material in the resinous binders which adversely effects photosensitivity. Additionally, some of the hole transport layer glass transition temperatures are near, or below room temperature thus constraining these devices mechanically, and limiting their use.
While the above described photoresponsive devices are suitable for their intended purposes, there continues to be a need for improved devices. Additionally, there continues to be a need for improved transport materials, especially those transport materials of improved solubility in the resinous binder, which solubility is believed caused by the presence of an ether linkage. Further, these materials possess excellent hole transport properties in view of the presence of aromatic tertiary amine groups. Also, there continues to be a need for improved overcoated photoresponsive devices containing a photogenerating layer, and a charge transport layer comprised of novel aromatic compositions containing an ether linkage, or ether linkages, which compositions have improved solubility in resinous binders within which they are present, and excellent hole transporting properties. Improved solubility enables loading of the hole transport molecule at 90 percent by weight in the resinous binder, without adverse crystallization occurring. Furthermore, the glass transition temperature of the aromatic ether compositions are above room temperature enabling the resulting devices to maintain desirable mechanical properties.
Furthermore, there continues to be a need for improved photoresponsive devices containing easily prepared novel hole transport molecules. Also, there continues to be a need for improved photoresponsive imaging members containing improved transport materials, and wherein these members are responsive in the visible and/or infrared region of the spectrum. Moreover, there continues to be a need for improved photoresponsive devices with a hole transport layer comprised of aromatic ether compositions situated between a photogenerating layer and a supporting substrate; and for photoresponsive devices with sensitive layers comprised of inorganic photogenerating compositions, and organic photoconductive compositions situated between a hole transport layer, and a supporting substrate.